Add eunit test for match validation of an flow modification message

OpenFlow 1.3.2 introduces a constraint that oxm_mask bit cannot be set to 0
if the corresponding in the oxm_value is set to 1. Such a condition is an error
indicated by bad_match/bad_wildcards.
(Motivated by #142).
Add validating mask of the match field in a flow modification message

OpenFlow 1.3.2 introduces a constraint that oxm_mask bit cannot be set to 0
if the corresponding in the oxm_value is set to 1. Such a condition is an error.
(Motivated by #142).
Add controller's scenario for sending flow mod with malformed mask in a match

This scenario helps to verify that the controller sends an error while receiving
flow mod with badly formed mask in a match filed of a flow modification message.
(Motivated by #142).
Refactor linc_us4_flow:validate_match/2

After introducing a new check the function was really unreadable.
(Motivated by #142).
Merge pull request #156 from FlowForwarding/issue142

Validating mask in OXM TLV